Astronomy

TRIANGULUM

ARIES

ANDROMEDA

M33

_

`

b

a

f

7 Trianguli

15

Trianguli

14 Trianguli

R Trianguli

5°

64 ASTRONOMY • DECEMBER 2018

s an avid angler, I

prefer small ponds

over large lakes and

reservoirs. Fishing

a large body of

water can be a daunting task.

With hundreds of acres to

explore, I could never cover all

the hot spots in a day’s time. A

5- to 10-acre pond, on the other

hand, can be easily covered in a

matter of hours.

It’s the same situation when I

switch from fishing to observ-

ing. I prefer to “paddle around”

a small constellation like

Delphinus or Lyra, rather than

ride the high seas in a vast stellar

aggregation like Virgo or

Ophiuchus. With that in mind,

let me invite you to one of the

night sky’s smallest “ponds,”

Triangulum, whose 132-square-

degree area is one-tenth that of

the largest constellation, Hydra.

If you’re not sure of

Triangulum’s location in the

night sky, refer to the StarDome

map in the center of this maga-

zine. From mid-northern lati-

tudes, Triangulum appears high

in the December evening sky

between Aries and Andromeda.

Punctuated by three stars

arranged in the form of a long,

narrow triangle, this constella-

tion is aptly named. It is made

up of Alpha (α) at magnitude

3.4, Beta (β) at magnitude 3.0,

and Gamma (γ), which shines at

magnitude 4.0. Gamma is

attended by the 5th-magnitude

stars Delta (δ) and 7 Trianguli.

This optical triplet can be

glimpsed with the naked eye

under a dark sky, and it is an

OBSERVINGBASICS

BY GLENN CHAPLE

Treasures in

Triangulum

The Triangle constellation may be small, but it’s packed

with a wealth of worthwhile targets.

Iota (ι) Trianguli — also

known by the Flamsteed desig-

nation 6 Trianguli and the

Struve double star designation

Struve 227 (STF 227 or Σ227)

— is a neat double star whose

magnitude 5.3 and 6.7 compo-

nents are separated by 3.7". One

of the 110 entries on my Double

Star Marathon list, it’s rapidly

disappearing in the west during

the March/April time slot when

the Marathon is being con-

ducted. Catch it now while it’s

more conveniently placed. I

recommend a magnification of

at least 75x for a clean split.

While Iota is still in the eye-

piece field, look about a half-

degree eastward. You should

spot a stellar pair that only a

seasoned double star observer

can see. This is Struve 232 (STF

232 or Σ232), a near-twin sys-

tem (magnitudes 7.8 and 7.9)

with a 6.5" separation. How

unfortunate that hundreds of

eye-pleasing pairs like this go

unobserved because of their

relative faintness. A bright

showpiece double like Albireo

(Beta Cygni) has the in-the-

face visual impact of a snow-

capped mountain peak; STF

232 possesses the delicate

beauty of a single snowflake.

Tria ng u lu m’s key center of

attraction is the Pinwheel

Galaxy (M33). Notorious for its

elusiveness, M33 spreads the

light of a 6th-magnitude star

over an oval-shaped area that

exceeds that of a gibbous Moon.

Surprisingly, M33 is faintly vis-

ible with the unaided eye and

relatively easy to spot through

binoculars, provided you view it

from an area free of light pollu-

tion and atmospheric haze. The

problem occurs if you try to

view M33 with a telescope and

high-power eyepiece. Instead,

work with a telescope and eye-

piece combination that pro-

duces a field of view 2° or more

across. My best view of M33

came with a 4-inch rich-field

scope and magnification of 30x.

Does my penchant for small

constellations mean that I avoid

the large ones? Hardly! In a few

months, I’ll take you to Hydra

to demonstrate how to break

down an expansive constella-

tion the way an angler dissects

a large body of water.

Questions, comments, or

suggestions? Email me at

[email protected]. Next

month: It’s a bird! It’s a plane!

It’s Super Moon! Clear skies!

eye-catching sight through 7x

binoculars or finder scopes.

Some 15° east of Delta is

another triangle formed by the

5th-magnitude stars 14 and 15

Trianguli and 6th-magnitude

HD 15755 (shown in orange).

Their spectral classes are K5,

M4, and G5, respectively, so

you’ll want to compare their

colors through binoculars or a

telescope. 15 Trianguli is a dou-

ble star with a wide separation

of 142". Its companion is a mag-

nitude 6.8 A-type star, produc-

ing a striking color contrast.

Slightly east and 0.5° south of

15 Trianguli is the long-period

variable R Trianguli. Over an

average of nine months, this

pulsating red giant’s magnitude

ranges from a maximum of 5.5

to a minimum of 12.5 and back.

According to “Bulletin #81” of

the American Association of

Variable Star Observers

(AAVSO), R Trianguli is cur-

rently brightening to an early

February maximum.

If you’ve never watched a star

undergo a dramatic change in

brightness, give R Trianguli a

look-see once a week. You can

create your own chart showing

R Trianguli and the magnitudes

of nearby comparison stars

by logging on to the AAVSO

website (aavso.org), or you

can email me for a chart that

I’ve put together.

A

BROWSE THE “OBSERVING BASICS” ARCHIVE AT http://www.Astronomy.com/Chaple.

Triangulum is one of the smallest constellations in the night sky. But despite its modest

size, it affords informed observers many rewarding sights. ASTRONOMY: ROEN KELLY

Glenn Chaple has been an

avid observer since a friend

showed him Saturn through a

small backyard scope in 1963.

Let me invite you to one of the night sky’s

smallest “ponds,” Triangulum.